The present invention relates to a wide-angle image pickup lens system for electronic cameras, which has a particularly short focal length and is of compact and simple structure comprising a reduced number of lenses.
In recent years, electronic cameras (digital cameras) have attracted attention as cameras of the next generation that supersede silver halide 35 mm-film cameras (usually called Leica size cameras). The size of image pickup devices used on such digital cameras is only a small, or very small, fraction of that of silver halide 35 mm-film cameras, as expressed in terms of diagonal length. To obtain images having the same angle of field, therefore, it is required to reduce the focal length of an image-forming lens system in proportion to that. Theoretically, the size of the lens system becomes small, correspondingly, and so component elements become small, too. Lens processing is thus extremely difficult. In view of the characteristic features of an electronic image pickup device, on the other hand, it is desired that the angle of emergence of rays from the image-forming lens system be as vertical to the image pickup device as possible. Thus, it is difficult to use conventional wide-angle lens systems (e.g., retrofocus lens systems) for silver halide 35 mm-film cameras (usually called Leica size cameras) directly on digital cameras.